Secret radio signaling system



Dec. 7, 1948. D. SARNOFF SECRET RADIO SIGNALING SYSTEM Filed Oct. 12; 1945 5 Sh eets- -Shee't 1- L6. COLT. COL-8.0

com. 00:..2. ooLa,coL.4. comco L INVENTOR DAVID SARNOFF ATTORN EY Dec. 7, 1948.

Filed 0st. 12, 1945 "fERMmAI. OFFICE D; SARNOF F SECRET RADIO SIGNALING S YQEEM 5 Sheets Sheet 2 FIG.2.

r M i i) RADIO TRANSMITTING STATION I 6 r k j PAGE. W MOTOR FAOSIMILE 20 SCANNER 1 RAO|0 l8 I f l TRANS. 8 O l4 6 I600 2000 my Sm so. "my

TONE LINE TERMINAL OFFICE FI 6.3. r k i RADIO RECEIVING F STATION I? 2| 0 g PHOTOGRAPHIC 5 smc PAGE RADIO MOTOR FAGSI r4 ILE RECEIVER SCANNER l w .L'i"*- STANPARD DEMOIDULATOR v OOMBINER RECEIVER I INVENTOR v 23 Ton: LINE DAVID SARNOFF ATTORNEY Dec. 7, 1948; D. ISLARNOFF 2,455,443

SECRET BADIQ S IGNALING SY -T EM Filed bet. 12, 1945 S Sheets-Sheet a 001.1. 001.2; cow M. com 00!... 33%? Q A FIGS 2 I CHARACTERS 9 4 LTRS o 'rRAus'mT'rme I E82 201%? 7 CAR LINE P RET FEED INVENTO'RV VH3 SARNOFF I BY.

ATTORN EY Dec. 7, 1948. D. SARNOFF 2,455,443

SECRET RADIO SIGNALING SYSTEM. I Filed Oct. 12, 1945 5 Sheets-Sheet 4 TRMINAL OFFIGE RADIO TRANSMHTTIN G I s'mnow L SYNC TAPE V 1 SCANNER 6 M010 'TRANS. 1+ v. 54 5a M so so/v P USH FREQUENCY MAINS PULL SHIFT -5 TONE LINE TERMINAL OFFICE Fl G. 6. i RADIO REcl-iwme v ,5 I STATION $YNO SYNC I L I LINE TONE 90 N 82 v oAvm SARNOFF BY ATTORNEY r i MQTOR OOMMUTATOR 70 A A RADIO RECORDER RECEIVER 78 N N 7 1m 8Q FREQUENCY 30w LINE SHIFT RADIO MAINS Amru lzn comm RECEIVER INVENTO'R Dec. 7, 1948. D, SARNQFF SECRET RADIO SIGNALING szsmm Filed Oat. 12, 1945 5 Shee'ts-Sheet 5 tub-2E. 10km lNVlNTOR DAVID SARNOFF ATTORNEY Patented Dec. 7, 1948 UNITED STATES PATENT crew-e1 David Sarnofi,.New. York, N .Yl, assignor to Radio Corporation of'America, a corporation of "Dela.-

ware Application-October 12, 1945*, seria'l'Noi 622,043

. 2 Claims.

This invention: relatesrto. an: improved: method of and system for secret-signaling;- i

Many systems andmethods havebeenproposed for obtaining, secrecy in. radio telegraphic signaling. They: include the telegraphic transmission of messagesin;accordance with a secret. code; interlacing, at thetransmitter; telegraphic elements of several messagesandkla ter, at.;the receiver, .unscrambling the. receilvedm-multiplexed signals; rapid switching. ofsuccessive-portions of a message from one signalingnhanneltto another. at predetermined, variable rates; mixing: codecharacters, suchas'may be used-to. actuate a teletypewriter; with telegraphic elements. derived- .fcronra tape inwhich amasking signalyhas been punched; and others. A

The degree .ofsecrecy attainable with such arrangements of the-prior artisrnot high jfor they can-be, and actually have. been. solved. with relative ease. to. yield thesupposedly secret messages, In addition, when: employing; long. distance. radio circuits asthelink between: transmitter andrea ceiver, such systems are. particularly, susceptible toinaccuracies brought abouthystat'ic and-fad.-

i'ng. Static impulsesrprolduceial'se markings and,

similarly, fading conditions. cause. dropouts or spaces. The end'resultioffb'o'th static. and timing is, therefore,.., to produce erroneous characters which are indistinguishable from desired signal transmissions;

To overcome these'faults is the. principal'purpose of this invention. More specifically, it is an ohjectof the invention to provide a secret signaling system which shallbe exceedingly difli'cult to decipher and which shall be substantially free of errors heretofore causedby iading,.static. or. other unfavorable conditions in the transmitting, medium. Briefly accordance. the invention, a standard keyboard. transmitter. at. a senderfs of.- fice is designedfto. print. pictorial; characters. or other arbitrarily chosen symbols. rather than the usual; letters. of. the. alphabet. Messages consisting of. theprinted symholsare then. transmitted by facsimile or by television over a radio. circuit, which. maybe operated by a. public carrier, to. the receiving. point. There, the. pictorial'j representations. reproduced, by facsimile or television, are read and. translated. Translationis efiected, in accordance. with. one modification of. the invention, by-meansof a. complementary. typewriter or printer. wherein hand; operated; keys. are marked with the. symbols,, but/the. type. printed. normal...

By: Dre-arrangement between. sender. and; ad;-

- 2? p dresseethesecretcombination of' symbols can be changed as often as desired so as to. enhance secrecy, even as against the carrier. Although static, fading. and similar adverse signaling-men- 5 ditions may produce distortions in the. pictures reproduced. at the receiving. end. of. the-system; each picture,.representing= alet'tr or wordrot-t'he message, will be clearly identifiedi as a..-whole, thereby enabling the. printing of. correct signal elements. In this way errors normally caused by static and: similar troublesome conditions are circumvented...

In. a. modificationx of the invention, which will be: described-in greater detail..later, relatively obtions. are. utilized. to cause automatic translation or printing of the transmitted. message. In. the event that thereceived. pictures re disfigured by reason of poor signaling conditions,. eachpicture, nevertheless,., is clearly recognizable in. its entirety and may berepaired'by means. of-suitable templets..before. use in.- mechanism. for. automatically printing. the messages. tram the. corrected, accurate, radiofacsimilel copy In..the more: detailed. description. of the present invention which follows, reference will be made to theaccompanying.drawings whereinz. 1

Figure. 1. is a special. code. devised; for. use in the present invention. Unlike symbols or'pictoriallrepresentations. thereoflrepre'sent different units of. intelligence, such as. letters of the. alphabet,. to he transmittediin secrecy; a

Figures 2. and. 3. areschematic representations, respectively,: of. page facsimile radio transmitting and receiving stations of a secret signaling system whichma-kes use of a. code. such as illustrated in Figure. 1; h

Figure 41 illustrates a secret code especially designedto enableautomatic translation andlprintjing .of secretv messageaalthough itishoul'd be understood that messages in. the: code of Figure .4 he translatedin accordance with the-pro.- cedure: employed. in. connection with Figures LI 2 and3f;.-

Figures 5 and-6 are, respectively, schematic diagrams of transmitting and. receiving apparatus forv messages sentby asecret codesuclr as: shown inFigure 4;. and.

Figure '7. is a simplified,- diagrammatic showing ofapp-aratus for automatically translatingiamessaga. composed of. the secretsymbolsof. Figure. 4, into. normal .printi.

The page facsimile. system ot Figureszand :3 makes use ofla secret. codesuch-asshown-in Fig.- ure I wherein eachrunit of intelligence to be scure-v differences between. pictorial! representatransmitted is delineated by a separate and distinct symbol or pictorial representation. In columns I, 3, 5, 7 and 9 of Figure 1 are shown the units of intelligence to be transmitted, such as letters of the alphabet, numerals, etc., and the symbols representing them are shown adjacent in the even numbered columns. Thus, for example, the letter C isv represented by a rectangle, letter R by a pair of vertical parallel lines, number I by a rhomboid, etc.

The coded copy of the message to be sent in secrecy is prepared by a printer or typewriter illustrated diagrammatically at 2 in Figure 2. The key caps of printer 2 bear the marks appearin in the odd numbered columns of Figure 1. The type faces on the keys of typewriter 2 are so set up, however, that in one case position the secret symbols of the even columns of Figure 1 are printed; whereas, in the other case position, normal printing, such as appears in'the odd columns of Figure 1, takes place when the typewriter is operated.

When sending a secret message, printer 2 is actuated so that the name and address of the addressee and also, if desired, of the sender, are i typed in normal print on a page inserted in the typewriter. To print the body of the message in accordance with the secret code of the even columns of Figure 1, the operator merely shifts case, by depressing the case shift lever, and then operates the key levers in the usual way.

After the typist has prepared the coded copy, it is transmittedby page facsimile over the radio circuit; When received at the distant receiving terminal, such as diagrammatically illustrated r in Figure 3, the radio facsimile copy may be delivered by the public radio carrier to the addressee, at whose office the secret; coded message is translated. Translation is effected by means of a typewriter 3 having the secret symbols or pictorial representations marked on its key caps and corresponding letters or other normal units of intelligence on its type faces. To heighten secrecy, the sender and addressee may change codes in accordance with prearranged, confidential schedules.

The set of pictorial representations of Figure 1, it should be clearly understood, is only illustrative. Many others can be devised and these may, of course, include actual pictures of different animate and inanimate objects. The representations chosen, however, should be such as can be used on type face and, when scanned, should be satisfactory for transmission over the radio circuit.

Returning to Figure 2 of the drawings, after the page copy of the secret message has been prepared in printer 2, it is transferred to a page facsimile scanner 4. The latter is driven by a synchronous motor 6 provided with motive power derived from a tuning fork standard 8. Preferably the amplitude modulation output of the scanner is converted to sub-carrier frequency modulation by a suitable converter [0 for transmission over a control tone line [2 which may be replaced, if desired, by an ultra high frequency radio relay.

At the output end of tone line 12, the frequency.

modulated sub-carrier is demodulated in'a demodulator M. The demodulated waves are used to control a reactance tube modulator l5 which causes a shift in frequency of the radio frequency carrier wave generated in radio transmitter l8. The carrier frequency may be shifted, for example, i2 kilocycles andradiated to the distant radio receiving system of'Figure 3.

l-IL

At the radio receiving station such as shown schematically in Figure 3, a two unit frequency diversity receiving system intercepts the frequency shifted carrier radiated by the transmitting antenna 20 of Figure 2. The two unit diversity receiving system includes the separated receiving antennas 5 and l and radio receivers 9 and H. The outputs of the latter are employed in a frequency shift combiner 13 to produce a frequency shifted subcarrier which is transmitted over a tone line It into the receiving terminal oflice. There the sub-carrier is demodulated by means of a suitable demodulator IT. The varying amplitude D. C. output of the demodulator is used to control a photographic facsimile page recorder I9 driven by synchronous motor 2|. The latter is supplied with synchronous power derived from a tuning fork standard 23.

The facsimile copy is then delivered to a customers office where a printer or typewriter 3, as before described, is provided for deciphering the secret, page facsimile message.

For more detailed descriptions of scanning machines and related apparatus which may be used at the transmitting terminal of Figure 2 and to photographic facsimile recording apparatus which may be used at the receiving terminal of Figure 3, reference is made to the book entitled Radio Facsimile, dated October 1938 and published by RCA InstitutesTechnical Press. Particular reference is made to pages 139, 144, 151, 172', 239, 240 and 241 thereof. For a detailed description of a suitable sub-carrier frequency modulation system for radio facsimile, reference is made to an article by R. E. Mathes and J. N. Whitaker entitled Radio Facsimile by Sub-Carrier Frequency Modulation appearing at page 131 of the RCA Review for October 1939. Systems wherein the outputs of diversity receivers are reduced to on-ofi keying by means of frequency shift combiners are described in U. S. Patents Nos, 2,067,432 and 2,070,418 issued to H. H. Beverage and in the copending application of R. E. Schock. et al., Serial No. 632,978, filed Dec. 5, 1945. A suitable frequency modulated sub-carrier demodulator such as used at M in Figure 2 and at l! in Figure 3 is described in U. S. patent to W. H. Bliss No. 2,350,869.

If desired, the secret message, typed on pages by means of printer 2, may be transmitted by radio television to a television receiver located near the translating typewriter 3. In that event, the operator of typewriter 3 would translate the secret symbols as they appear on the television screen.

Automatic translation and printing of messages, made secret in accordance with principles previously expounded upon in connection with Figures 1, 2 and 3, will now be described with the aid of, and reference to, Figures 4, 5, 6 and '7. The automatic system'involving these figures will enable one to dispense with the services of the typist heretofore required tooperate the translating typewriter diagrammatically illustrated at 3 in Figure 3.

For automatic operation, a special formation of secret symbols is provided so that scanning will produce an equal length code suitable for automatic translation at the receiving end of the system. The secretfacsimile code of Figure 4 illustratesby Way of example, a simple line formation which; when 'photoelectrically scanned, will produce the equivalent of an equal length teieprinter baud code for start-stop printer use. It will be noted that along the tops of the secret y it will equal twobaud's;

stream cli'aracters oi symbcls of colunis fi hand: 6, pips are positioned which-5 representthe marking elements of the'five unit: starte-stop Baudot teleprinter code. The-marking and spaci'ng elements shown are those necessary: for-selection: purposes. The space between'characters: must be such that as. Will be explained more fully later.

The units-off ihtell igenceto be: transmitted ap pear in. columns: I 33 and 5 nf-Figure 4. andi. the corresponding secret. facsimile. symbols:v are mediately: adjacent; in columns 2t 4"- andi. 6;; It will be I recognized: that the signaling: elements of Figure. 4a are. arranged? the. sequence generally adoptedifor. teletypewriters. i

Since: a. slip on tape. facsimil system. lends itself} more readily" to; automatic translation: re:- quirements, aasli'pl. omtapew typewriter ill is-xproiided: as; diagrammatically shown: in Figurei Typewriter '50: is constructed: so: that. the: lcey'caps are marked with:normal'iunits:ofiintelligencezsueh asiappear in the odd ficolumn'seofrll'igune handfthe type faces are embossed with; the symbols cit-col.-

- umrrss 2:; 14'1" and-16s. ltts'hould i herniated: thainb' lowercase characters, suchlasithe. letters; of column I, Figure 4, at the receiving. terminal. In other words, the same. facsimile, symbols are transmitted for eitherupper orlower case marks, shiitrf-rom one case to the: other being accom'- plished. by; actuation. ofthe. keys markedi FIGS or;-LTRS-3 at, the, transmitting; typewriter; 50.

The: entire message is printed, on the: tensor slip; fedto printer 50, in the form of the secret symbols of: Figure 4. The printed tapeeisathen transtenred w to the tape scannem 56 oflFigure 5 and photoelectrically scanned. Synchronous motor 52, powered from 60 cycle mains, drives the tape-scanner. For a more detailed description of a suitable tape-facsimile scanning system which may be used at this point, reference is made to page 271 of Radio Facsimile previously referred to.

As indicated in Figure 5, the control voltage output of scanner 56 is used to operate a push.- pull tone keyer 5B. The keyed tone output is fed over a tone transmission line 60, or by way of a radio relay link, if desired, to a frequency shift keyer 64 in turn controlling the output of a radio transmitter 66. The carrier wave radiated by antenna 68, connected to radio transmitter 66, is shifted in frequency, in accordance with the output voltage of scanner 56, by keyer 64. This shift in frequency may be any desired amount such as $425 cycles per second.

The frequency shifted radio carrier wave, radiated by antenna 68 of Figure 5, is received at the radio receiving station of Figure 6. The latter includes spaced receiving antennas I0, I2 feeding super-heterodyne radio receivers I4 and H5. The detected outputs of the receivers I4 and I6 are reduced to on-off keying ofa suitable tone frequency, alternating current by means of the frequency shift combiner I8. The on-off keyed tone is transmitted to the receiving terminal oflice of Figure 6 over a control link which may be an ultra high frequency radio circuit or, as illustrated, a wire tone line 00.

At the receiving terminal of Figure 6, the incoming on-off keyed tone is amplified by line amplifier 82? and fedi. ins. amplified formg, totape reccrder- 8.43. As-Lmor sv fully described. ina paper mit-led .Tapes. Facsimile Synchronizing Sys tems by Henry Shore' andJ'ames Nrwhitaker at page? 2762 of; Radioz Facsimile, previously referredto, recorder; Mtbriefly', comprises arevolving spiral memberand a signal controlledrecording: bar; The? ban; or moving element of the reoordingheadg is: arranged topress a white record tape: and; a'. carbon. slip: together in a pattern which results'eimant exact facsimile of that which obtains: the-scanningprocess 1 carried on at the tape scanner. 56 oil ng-111286; V

AS ShOWH" in Figure i and as more fully described:Radio Facsimile at page 281,.the tape recorders of. Figure 6; is: provided. with. a special. synchronizing commutator 86 and-- is driven by synchronous motor 88: powered: from 60 cycle: alternating. current mains 90;:

The messages onvthe facsimile tape; derived from; tape recorder 84 of- Figure- 6'; will be inscribed: hr the secret symbol code of Figure. 4. Thertapeeis then. subjected to; a. local seaming operation to provide equal: length band signals, arranged in successive-equal; time-intervals; The equalzlength baudr signals; fedrto afive unitstartstop teleprinter, actuate the same causingtraces lation', i. e;, printing of the secret message in normal type. An arrangementfor scanning the tapera-nd applying the equal length baud signals toa fiveunit start-stop printer'is schematically illustrateddn Figure" 7.

Before. describingiliigure 7 indetail, it. should bebornein mind: that a standard. start-stopfive unitteleprinter functions at. 368- operations per minute. Thatis, it. transcribes and. prints 368 seven: unit baudgroups-per minute. Successive equal time. intervals are assigned tothe sevenlunit baud] groups. Five of the; seven. units. arenecessary and used for character selection purposes; The sixthunit of eachgroup is useclv to provide. for the stop function in the printer, i. e., printing and clearance. The seventh provides the start function, i. e., it conditions the printer for the next operation.

Returning now to Figure 7, the facsimile slip or tape record I00, on which the specially formed symbols of Figure 4 have been recorded by recorder 84 of Figure 6, is passed through a scanner, as shown in Figure 7, so arranged as to scan the top portion of each character. Passage of tape I00 through the scanner is effected by the action of the tape feed wheels I02, I04 in turn driven by gearing I06. The latter is rotated by motor I08. A scanning spot III], produced by light source H2 and a pair of lenses H4 and H6, is directed on the upper portion of each symbol. Light reflections from the tape pass through a lens II8 which concentrates and directs the reflected light upon a photocell I20. Photocell I20 controls the output of a vacuum tube amplifier I24 which controls a polar relay I26. The tongue of the relay is connected to supply suitable voltages of opposite polarity to, and thereby operate, a standard five unit start-stop teleprinter I28.

Drive motor I08 should be designed and operated to pull the tape I00 past the scanning spot I I0 sothat 368 seven unit baud groups will be scanned per minute. By means of gearing I06, worm I30 and shaft I32, motor I08 is made to rotate a shutter I34. Shutter I34 is so positioned and dimensioned that at the end of five baud units of each seven unit group, the light source will be cut off for one band length. At the end of that time, it will be observed, light spot IIO will hit a white space between the characters for a time equal to one baud. These in between character bauds provide, first, the stop function in printer I28 and, second, the start function.

Instead of using a five unit code and printer, a synchronous seven unit printer and a balanced code may be used to good advantage. When using such a balanced seven unit code, the minimum spacing'between characters should be three bauds and the maximum seven for single channel operation, For a detailed description of a balanced code seven unit system, reference is made to U. S. Reissue Patent No. 2 2,394, issued to J. B. Moore et al. For printing apparatus particularly suited to the use of a balanced seven unit code, reference is made to the following U. S. patents issued to J. A. Spencer: 2,153,737, 2,231,- 397, 2,274,103, 2,336,197.

Obviously, the pips giving rise to the impulses for automatic operation may be arranged othersecret symbols, markings on different symbols being arranged in accordance with an equal time interval multi-unit code, different markings representing different units of intelligence to be transmitted, means for transmitting the symbols by facsimile over an alternating current circuit to a distant receiving point, means at the receiving point for reproducing a facsimile copy of the secret symbols from the received currents, means for photoelectrically producing electrical current impulses from the facsimile copy, the impulses being arranged in equal time intervals in accordance with the multi-unit code used during transmission, thereby circumventing errors introduced by the alternating current circuit, a shutter so dimensioned, positioned and actuated as to operate said photoelectric means in such a way as to provide in between character current impulses and means for utilizing the impulses so produced to cause printing of the message in normal type.

2. A secret signaling system comprising, in combination, a typewriter at a transmitting point, said typewriter being provided with keys and type faces such that in one case position, the address of the addressee may be printed in normal type and such that in the other case position, secret symbols are printed, said secret symbols representing different letters of the alphabet whereby a secret message may be printed following the printing of the address of the addressee in normal print, said secret symbols being so chosen as to be satisfactory for clear transmission over a radio facsimile circuit, a radio facsimile system for transmitting messages so typed up to a distant receiving point whereby errors and inaccuracies due to fading conditions and static impulses are avoided, and instrumentalities located at the receiving point for translating the secret symbols as received by radio facsimile into normal type.

DAVID SARNOFF.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,870,989 Eldred Aug. 9, 1932 1,973,539 Morton Sept. 11, 1934 2,337,553 Hofgaard Dec. 28, 1943 2,376,111 Bacon May 15, 1945 2,397,202 Potts Mar. 26, 1946 2,406,811 Deloraine Sept. 3, 1941 

